Final answer:
The most essential pre-installed program on a new laptop for immediate use is an Internet browser, as it enables the user to access the web and download any other required software.
Step-by-step explanation:
When Hector is looking to purchase a new laptop and wants to use it immediately after buying, the most important pre-installed program to check for is an Internet browser. While other applications such as Microsoft Office, antivirus software, and an email client are important, they are not essential for the initial use of the laptop. An Internet browser is crucial because it allows Hector to search the web for any additional software or information he might need right away. Most laptops come with a pre-installed browser, which facilitates instant access to the internet to download other necessities.